2003 W209 CLK, 2005 R171 SLK, Volvo XC40 P8 Twin Motor Pro EV
Does it currently have a CD changer? If you are just replacing a faulty one then no problem. If it does not have one you will need an extra connector for the wiring loom. I think it needs to connect to the system somewhere in the nearside footwell and also to the head unit itself. As far as I know it will not need coding.
2003 W209 CLK, 2005 R171 SLK, Volvo XC40 P8 Twin Motor Pro EV
Here is a link to the wiring kit. If it has command then a different kit is needed.https://www.commandonline.co.uk/CD-wiring-kit-for-D2B-W203-W209-C-CLK-without-COMAND.html